The purpose of this research project is to better define and characterize the molecular genetic basis and uniqueness of rheumatoid factor (RF) expression in rheumatoid arthritis (RA). Synovitis is central to the immunopathologic events in RA, thus it is likely that RF made there are of greater pathogenetic importance than serum RF. In particular, we have identified RF produced by rheumatoid synovial cells (RSC) that are not detected in and are 10-1000 times more avid than autologous serum RF. To examine RSC RF more critically, hybridoma derived human monoclonal IgM RF (mRF) will be generated by fusing RSC with a mouse/human heterohybrid (F3B6) fusion partner. The IgG subclass specificities and affinities of these human mRF will be determined using a modified enzyme immunoassay (ELISA) and will be matched with gene sequences and idiotypes (id). The heavy (H) and light (L) chain variable region (Vr) genes for each of the human mRF will be cloned and sequenced using the polymerase chain reaction (PCR). Anti-idiotypes (alpha-id) will be used to determine expressed gene products and their uniqueness in RA patients relative to family members, normals and other RF disease controls (cDNA probes cannot provide this type of information). Primary structure dependent idiotypes (ids) on human mRF will be characterized and corresponding synthetic peptides will be made to conformationally dependent ids expressed on RSC hybridoma derived human mRF. The primary structure dependent alpha-ids and the conformationally dependent alpha-ids will be used as probes to examine the uniqueness of expression of these RF ids in RA. The data generated from this proposal should provide critical new information about the molecular genetic basis and uniqueness of RSC RF in RA and should provide particularly exciting comparative data for similar types of determinations in other RF-associated diseases (i.e., B cell malignancy and Sjogren's syndrome). Moreover, information generated from this project may significantly enhance our understanding of the molecular genetic basis of autoantibodies in other autoimmune diseases.